<?php
header("Content-type:text/html; charset=utf-8");
require_once 'db_conn.php';
$conn;

$sql = "SELECT * FROM  t_message";
$result = $conn->query($sql);

$rows = $result->fetch_all(MYSQLI_ASSOC);

print_r($rows);
foreach ($rows as $value){
    echo "<br/>";
    echo $value['username'] ."说： " . $value['content'];
}